FIG. 28 is a sectional view of plasmon sensor 100 adapted for detecting, e.g. viruses which is disclosed in Patent Literature 1. Plasmon sensor 100 includes prism 101, metal layer 102 having a smooth surface disposed under prism 101, insulation layer 103 of a predetermined dielectric constant having a smooth surface and disposed under metal layer 102, and ligands 104 fixed to a lower surface of insulation layer 103.
A surface plasmon wave which is a compression wave of electrons exists on the interface between metal layer 102 and insulation layer 103. Light source 105 located above prism 101 applies p-polarized light to prism 101 under a condition of total reflection. At this moment, an evanescent wave is generated on surfaces of metal layer 102 and insulation layer 103. The light totally reflected on the surface of metal layer 102 enters detector 106 that detects an intensity of the light.
Here, if a matching condition of wave numbers is met under which the wave number of the evanescent wave is consistent with the wave number of the surface plasmon wave is met, energy of the light supplied from light source 105 is used to excite the surface plasmon wave, accordingly decreasing the intensity of the reflected light. The matching condition of wave numbers is dependent upon an incidence angle of the light irradiated from the light source. Therefore, the intensity of the reflected light decreases at a certain incidence angle when measured with detector 106 while changing the incidence angle.
A resonance angle at which the intensity of the reflected light becomes minimum depends on a dielectric constant of insulation layer 103. The dielectric constant of insulation layer 103 changes when an analyte which is a measuring-target substance in a test sample specifically binds to ligands 104 and form a product of specific binding under insulation layer 103, which in turn changes the resonance angle. This allows a binding strength, speed and the like of the specific binding reaction between the analyte and ligands 104 to be detected by monitoring the change in the resonance angle.
Plasmon sensor 100 includes light source 105 for supplying p-polarized light and prism 101 disposed on metal layer 102, thus having a large size and a complex structure.